Conventionally, as small-sized capacitors, multilayer ceramic capacitors, tantalum electrolytic capacitors, and aluminum electrolytic capacitors are in practical use. Among these, a multilayer ceramic capacitor uses as a dielectric body a complex oxide such as barium titanate having a large relative dielectric constant or strontium titanate having a high voltage resistance.
Electrostatic capacitance is in proportion to relative dielectric constant and is in inverse proportion to thickness of dielectric layer and therefore, there is an increasing demand for a dielectric layer having a high relative dielectric constant, which is thin and has a uniform thickness.
As methods for forming a dielectric layer, Japanese Patent Application Laid-Open No. 60-116119 (Patent Document 1) and No. 61-30678 (Patent Document 2) disclose technique for forming a thin film of barium titanate by chemically forming a metal titanium substrate in a strong alkali solution containing barium ions. Japanese Patent Application Laid-Open No. 05-124817 (Patent Document 3: related application: U.S. Pat. No. 5,328,718) discloses a technique for forming a thin film of barium titanate on a substrate by alkoxide method.
Japanese Patent Application Laid-Open No. 2003-206135 (Patent Document 4: EP1445348) discloses a technique for forming a composite titanium oxide film, in which a metal titanium substrate is treated in an aqueous solution of alkali metal to thereby form a titanate of alkali metal on the substrate surface and is further treated in an aqueous solution containing metal ions such as ions of strontium and calcium to thereby substitute the alkali metal with metals such as strontium and calcium. Further, Japanese Patent Application Laid-Open No. 11-172489 (Patent Document 5) discloses a method for producing a barium titanate film by forming a titanium oxide film on a substrate by electrochemical approach and then subjecting the film to anodic oxidation in a barium aqueous solution.                [Patent Document 1]            Japanese Patent Application Laid-Open No. S60-116119            [Patent Document 2]            Japanese Patent Application Laid-Open No. S61-30678            [Patent Document 3]            Japanese Patent Application Laid-Open No. H05-124817            [Patent Document 4]            Japanese Patent Application Laid-Open No. 2003-206135            [Patent Document 5]            Japanese Patent Application Laid-Open No. H11-174289